Photographic printer with automatic exposure control

ABSTRACT

Photographic printer is provided with an apparatus for controlling the quantity of printing light to be applied to a printing paper in dependence upon the variable densities of negative film to be printed. Said intensity control apparatus is composed to two photoelectrical devices, namely one for controlling the effective current supplied to a printer lamp and other for controlling other factors influencing the quantity of the printing light. A correction signal is derived from the former device and applied to the latter device, to thereby attain a fine and high speed control of the photographic printing process with proper exposure appropriate for the negative and printing paper as used.

United States Patent Yamada 1 Mar. 21, 1972 54] PHOTOGRAPHIC PRINTER WITH 3,237,516 3/1966 Shearer ..355/69 x AUTOMATIC EXPOSURE CONTROL 2,201,606 5/1940 Bing ..355/68 [72] Inventor: Yoshihiro Yamada, No. 2845, Aza Kuprimary Exami"er Samue| Matthews fOlShl, 0112a HlfaPar13 Tenpakwcho, Assistant Examiner-Monroe H. Hayes showa-kll. g y h Alchl'keflt Japan Attorney-Kane, Dalsimer, Kane, Sullivan and Kurucz [22} Filed: Mar. 13, 1970 ABSTRACT [21] Appl 19407 Photographic printer is provided with an apparatus for controlling the quantity of printing light to be applied to a printing [52] U.S. Cl ..355/69 paper in dependence upon the variable densities 'of negative [51] lnt.C1. G'03b 27/76 film to be printed. Said intensity control apparatus is com- [58] Field of Search ..355/68,69 Posed to two photoelectrical devicesnamely one for trolling the effective current supplied to a printer lamp and 56] References Cited other forcontrolling other factors influencing the quantity' of the printing light. A correction signal is derived from the UNITED STATES PATENTS former device and applied to the latter device, to thereby attain a fine and high speed control of the photographic printing 2,794,366 6/1957 Canady ..355/68 process with proper exposure appropriate for the negative and 2,444,675 I 7/1948 Rath ..355/68 priming paper as used 2,995,978 8/1961 Glandon ,...355/68 2,835,165 5/1958 Smith ..355/68 1 Claims, 3 Drawing Figures AC. Source 12 i TNT 5" Llqht Source Purse Amplifier t? Negative Ho 1 c1o r iii 1 I Correction Siqnul Generator 4 :Photo Detector 0,6, Source l6 l9 Optical System g' TZOT 15 X Phmogmphw Utilization Switching Exposure Input of Printer l 5 6 PEP-'- U it Circuit Control g z l 14 l 13 i 1 Beam Splitter 7 Integrator 5 Photo P Qintinq Poporl PHOTOGRAPI-IIC PRINTER WITH AUTOMATIC EXPOSURE CONTROL BACKGROUND OF THE INVENTION The present invention relates to a photographic printer with an apparatus for automatically controlling the quantity of printing light to be impressed on a printing paper in dependence upon densities of negative originals to be printed or copied.

As is well known, the quantity of the printing light is a function of the intensity of the light and the length of the period during which the printing paper is exposed to the printing light, namely, the length of the exposure time. p

In a hitherto known photographic printer of the type as above mentioned, the quantity of printing light applied onto the printing paper has been regulated by means of a photoelectrical apparatus which operates to vary the intensity of the printing light in dependence upon the density of the negative to be printed, while the exposure time is maintained constant. This kind of photographic printer has disadvantage that the precise or reliable printing can not be accomplished because of a slow responsibility of the printing lamp to the intensity control signal from the electronic apparatus. Furthermore, the constant exposure time must be so selected, that even a negative original having the greatest density can be printed with a printing lamp having an available maximum light output. Accordingly, a remarkable long exposure time is required also for the negative having a reduced or thin density, as a result of which a lot of time is expensed for the whole printing treatment.

Another type of the priorly known photographic printer has a photoelectrical apparatus for controlling the exposure time or period as a function of the variable densities of the negatives with the intensity of the printing light held constant. In this type of the photographic printer, the exposure time is varied within a relatively wider range depending upon the average density of the negative film to be printed, and the SchwarschiId-effect therefore becomes remarkable particularly in case of the thick negative.

SUMMARY OF THE INVENTION Accordingly, an important object of the present invention is to provide a photographic automatic printer, in which the disadvantages of the conventional printers as above-mentioned are eliminated.

Another object of this invention is to provide a photographic printer which allows a shorter exposure time and hence a speedy printing with an optimum intensity of the printing light.

Still another object of this invention is to provide an improved apparatus for controlling the intensity of the printing light and (or) the exposure time in dependence upon the densities of negative films, to thereby enhance the speed of the printing operation.

These and other objects of this invention can be attained by providing a photographic printer comprising a printing light source, an optical system for projecting the image of an original to be printed onto a printing paper, first means for controlling the intensity of said printing light in dependence upon the density of the original, second means for controlling the quantity of the printing light to be applied to said printing paper as a function of the intensity of said printing light and various photographic, electrical and/or mechanical factors, and third means connected to said first means for producing a signal which is applied to said second means as a correction signal to additionally control said second means.

BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other'objects as well as the advantageous features of this invention will become more apparent from the following description of a preferable embodiment of this invention taken in conjunction with the annexed drawings, in which,

FIG. 1 is a block diagram of a preferable embodiment of a photographic printer control system according to this invention,

FIG. 2 is a schematic circuit diagram of a switching apparatus which can be conveniently employed in the control systems shown in FIG. 1, and

FIG. 3 is a circuit diagram of a printing light quantity controlling circuit which can be preferably employed in the printer control system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, referring to FIG. 1, reference numeral 1 generally indicates a photographic printer which comprises a light source or electric lamp 2, a negative supporting holder 3 for support ing a negative film to be printed, and an optical system 4 for projecting the image developed in the negative film onto a printing paper 5 by way of a shutter 6 for setting the exposure time. Disposed between the shutter 6 and the printing paper 5 is a beam splitter 7 which is adapted to divert a portion of the printing light for the purpose which will be hereinafter mentioned. Such photographic printer is well known for those skilled in the art and therefore more detailed description will be unnecessary.

A photo-detector 8 which constitutes a part of the circuit for controlling the intensity of the printing light is disposed below the negative holder 3 in a suitable position for receiving light emitted by the printer lamp 2 and passed through the negative film supported on the holder 3. This photo-detector serves to produce an electrical signal having a magnitude proportional to the intensity of the light impinging thereon, which intensity in turn will depend upon the density of the negative to be printed. Such photo-detector 8 can be composed of a conventional element such as a photocell, photoconductor, photomultiplier, etc. The output from the photo-detector is applied to an amplifier 9, the output from which in turn is connected to a pulse generator 10 which is adapted to produce a train of pulses having variable durations in dependence upon the amplitude of the electrical signal from the amplifier 9. The pulse generator 10 may comprise a phase shifter, a pulse producing unijunction transistor and a pulse transformer having two output or secondary windings. The output pulses from the secondary windings of the generator 10 are applied, respectively, to gate electrodes of a pair of silicon-controlled rectifiers or thyristors which are connected in antiparallel with each other between alternating current source 12 and the printing lamp 2, said thyristors constituting an intensity control circuit 11 ofa phase control type.

The operating manner of the above mentioned light intensity regulator apparatus will be self-explanatory. In brief, this regulator apparatus operates to regulate, namely increase or decrease the intensity of the printing light in dependence upon the density of the negative film by controlling the quantity of the energizing AC current supplied to the printing lamp 2.

The photographic printer 1 has furthermore another the 13 such as photocell, photoconductor, photomultiplier. etc.. which is so disposed hereinafter it can receive a portion of the printing light partially reflected from the beam splitter or mirror 7 having a half-transparency. The photoelectric element 13 is connected to an integrator circuit 14 comprising a charging condenser, the charged potential of which is varied in dependence upon the photoelectric current intensity produced in the element 13. The output from the integrator 14 is applied to a switching circuit 15, the states of which can be controlled by the level of the output signal from the integrator 14 and a control signal from an exposure control circuit 16 which will be hereinafter described in detail.

FIG. 2 shows a switching circuit 15, which comprises an electronic tube or triode 21 having a control grid connected to the output of the integrator 14 and a cathode electrode connected to the exposure control circuit 16. The anode electrode of this tube 21 is connected to the energizing coil of a relay 22, having contacts 23 which are adapted to close or open, in response to the output signal from the switching tube 21, a line for supplying direct current to a utilization unit 18 such as an electromagnet for controlling the operation of the shutter 6.

The operating manner of the above-mentioned apparatus is as follows:

When a predetermined quantity of the printing light has been received by the photoelectric element 13 from the beginning of the exposure period and hence the condenser of the integrator circuit 14 has attained a predetermined potential level, the switching triode 21 is switched to the conductive state, as a result of which the relay 22 is energized to close the current supply line to the electromagnet 18, to thereby close the shutter. The exposure period is thus terminated. As is apparent for those skilled in the art, the switching of the triode 21 to the conduction state is a function of both the potential applied to the grid control and the bias voltage applied to the cathode electrode, which bias voltage is supplied from the exposure control circuit 16. In other words, the time span of the exposure period of the printer 1 as controlled by the shutter 6 depends upon the density of the negative film supported on the holder 3 and the level of the cathode bias voltage of the tube 21. In the priorly known exposure time control apparatus, this cathode bias is preset at. a predetermined poten tial in consideration of various photographic factors such as Schwarzschild-exponent and the photosensibility of printing papers to be used as well as such electrical and/or mechanical factors as drift of circuit parameters and inertia of the relay. Such presetting of the cathode bias is schematically indi'cated by a phantom block 24.

On the contrary, it is proposed according to the present invention to vary the level of the bias voltage applied to the cathode of the triode 21 in response to the variations in the density of the negative films. To this end, the exposure control circuit 16 is provided, a preferable embodiment of which is shown in detail in FIG. 3.

Now referring to FIG. 3, the exposure control circuit 16 comprises a series circuit of a DC source 31 and a switch 32. Connected in series therewith is a first potentiometer or voltage divider 33 comprising a variable resistor 34 with a movable tap or wiper arm 35, which is connected, by way of fixed and movable contacts C and B of a two-pole changeover switch 36, to the resistor 37 ofa second potentiometer 38 having a movable tap 39. Furthermore, a third potentiometer 40 comprising a resistor 41 and a wiper 42 is provided, which wiper 42 is electrically connected to a resistor 43 of a fourth potentiometer 44 having a wiper tap 45 which in turn is connected to the fixed contacts B, and A of the two-pole changeover switch 36. Other fixed contacts A, and B of the switch 36 are connected to the other ends of the resistors 41 and 43. The movable taps 35 and 42 of the potentiometers 33 and 40, respectively, are mechanically coupled with each other as is indicated by a broken line.

Referring to FIG. 1, connected to the output of the intensity control circuit 11 is a correction signal generator 17 of a conventional configuration which is adapted to produce a direct current signal having a magnitude proportional to the effective current to be supplied to the printer lamp 2. The correction signal produced by the circuit 17 is applied to the exposure control apparatus 16 between the variable resistor 41 of the potentiometer 40 at one end thereof and the tap 39 of the potentiometer 38. The output signal of the exposure control circuit 16 will appear at the movable contact C, of the switch 36 and is applied to the cathode electrode of the switching tube 23. It will be understood that the movable contacts C, and C of the two-pole changeover switch 36 are mechanically coupled to each other as indicated by a broken line therebetween.

The operation of the above-mentioned exposure control circuit 16 is carried out as follows:

After having disposed a standard or reference negative on the holder 3, the switch 32 is closed. The correction signal generator 17 produces a DC voltage corres onding to the density of the standard negative. This DC vo tage is supplied to the exposure control circuit 16 as hereinbefore mentioned. The potentiometer 38 is so adjusted in the position of the wiper 39 thereof, that a voltage V, appearing across the resistor 41 of the potentiometer 40 becomes zero volt. Next, the potentiometer 33 and 40, the wipers of which are mechanically coupled with each other, are so set that the satisfactory printing of the standard negative original can be effected on the printing paper 5 as used. These set'positions of the potentiometers 33 and 40 are determined by the various factors such as those hereinbefore mentioned. This is schematically indicated by a block 19 in FIG. 1. The photographic printer now comes to the state ready for printing various negative films. The switching-in of the changeover switch between the two positions A and B is selectively carried out, depending upon whether the density of negative to be printed is thicker or thinner than that of the standard negative. The potentiometer 44 serves for the manual adjustment of the output signal of the exposure control circuit 16, which output signal is applied to the cathode triode of the triode 21, together with the variable signal from the integrator 14 applied to the grid, to automatically control the switching time thereof in dependence upon the printing light intensity to thereby regulate the exposure time of the photographic printer.

In the foregoing, a preferable embodiment of the present invention has been described. However, it should be appreciated that various modifications of such embodiment would be possible for those skilled in the art without departing from the scope and spirit of the present invention. For example, instead of the shutter 6, an adjustable iris diaphragm or other device for influencing the intensity of the printing light such as filters may be employed. Furthermore, instead of the mechanical shutter, a switch such as the contacts 23 of the relay 22 can be disposed in the circuit for the energization of the printing lamp 2. The two photoelectrical elements 8 and 13 may be replaced by only one photoelectrical element for both the intensity control and the exposure control. ln place of the triode 21, other type of switching elements such as transistor discharge tube, etc. may be used. The selective switching of the changeover switch 36 may be carried out automatically by means of a suitable electric circuit in dependence upon the thickness or thinness of the negative film to be copied. Finally, the control signal from the exposure control circuit 16 may be added to the input of the integrator with the cathode bias voltage preset fixedly. Accordingly, it is not intended that the present invention is exactly restricted to the disclosed embodiment.

What is claimed is:

1. Photographic printer provided with a control apparatus for automatically controlling the quantity of printing light to be applied to a printing paper in dependence upon densities of a negative film to be printed and other factors such as sensitivities of said printing paper and electrical and (or) mechanical factors of the printer, said control apparatus comprising:

a first photoelectric converter for receiving printing light from a light source after it has passed through said negative film to adjust the intensity of said light source by way of an intensity control circuit;

a second photoelectric converter for receiving printing light after it has passed through an exposure time setting means to adjust the duration of exposure in dependence upon various photographic factors of light sensitive materials to be printed and electric and/or mechanical factor of said printer by way of exposure time control circuit including an integrator, and,

a correction signal generator having an input coupled to said intensity control circuit and an output coupled to said exposure time control circuit, whereby said exposure time setting means is additionally influenced by said light intensity control circuit. 

1. Photographic printer provided with a control apparatus for automatically controlling the quantity of printing light to be applied to a printing paper in dependence upon densities of a negative film to be printed and other factors such as sensitivities of said printing paper and electrical and (or) mechanical factors of the printer, said control apparatus comprising: a first photoelectric converter for receiving printing light from a light source after it has passed through said negative film to adjust the intensity of said light source by way of an intensity control circuit; a second photoelectric converter for receiving printing light after it has passed through an exposure time setting means to adjust the duration of exposure in dependence upon various photographic factors of light sensitive materials to be printed and electric and/or mechanical factor of said printer by way of exposure time control circuit including an integrator, and, a correction signal generator having an input coupled to said intensity control circuit and an output coupled to said exposure time control circuit, whereby said exposure time setting means is additionally influenced by said light intensity control circuit. 